Positron annihilation lifetime technique has been applied to study the
microstructural changes in steel after heat treatment (tempering process).
Positron lifetime spectra for the tempered samples in sandwich configuration
with the positron source were accumulated at room temperature using a
conventional fast-fast coincidence timing system. The measured lifetime spectra
have been analyzed. A correlation between the macroscopic mechanical
properties and the positron annihilation parameters has been established.
Meanwhile, with the aid of image analysis method, the American Standards for
Tools and Materials (ASTM) grain size in the tempered samples was
determined. The two state trapping model has been applied for interpretation of
the experimental results.